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new Madasgascar : dating problems



Message text written by INTERNET:jwillson@harper.cc.il.us
>Can anybody fill us in on a) just what is the problem in dating this? and
b) any possibility this problem can be resolved or worked around and some
"hard" dates produced for this??<

        Although I haven't yet seen the paper and can't comment on what it
does and does not say about the dating, from word around SVP, I understand
that the "Middle Triassic" date stems from two things:  (1) the lack of
diagnostic Late Triassic index fossils, such as phytosaurs and aetosaurs,
and (2) the primitive nature of the rhynchosaurs.  In other words, it's
based on (1) negative evidence and (2) "stage of evolution" arguments, and
_not_ on solid, definitive data.  However, I also understand that the
sandwich of sediments from which the fossils come spans a terrifically long
period of time, from the Permian through the Early Jurassic, much of which
is physically difficult to reach.  Some phytosaur scrap was reported from
some undetermined point in the sandwich by Dutuit (I think) years and years
ago, but without good provenance info; it remains to be seen if the
material is from the same place/stratum as the new dino material.  I also
do not know if a detailed stratigraphy of the sediments is available.

        'Twas wonderful to meet all those of you whom I had not met
previously around SVP!


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                     Jerry D. Harris
                 Fossil Preparation Lab
          New Mexico Museum of Natural History
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